The usefulness of a fiber optic transmitter module depends in part on the ability of the module to transfer light from the energy source into the optical fiber that transmits the light. Forming a microlens on the end of the fiber, i.e., a "microlens", improves transfer of light from the energy source to the optical fiber. There are limitations, however, in the current or known methods for forming such microlenses. For example, while many techniques exist to manufacture microlenses, none has both the flexibility to make a number of different types or shapes of microlenses and the ability to be used in a large-scale production environment. That is, while some techniques provide flexibility in microlens configurations, other techniques may be scaled for production. Present methods include techniques known by the following names: (1) draw and lensing; (2) mechanical machining; (3) laser machining; (4) bubble etch and lensing; and (5) taper etch and lensing.
In the draw and lensing technique, forming a microlens begins by attaching a weight or otherwise applying a pulling force on the fiber and then placing the fiber in an arc. The arc softens the fiber so that the pulling force may draw it to a taper. After fiber separation, the arc melts the tip to form a hemispherical microlens. A limitation of this technique is that it can only form hemispherical microlenses. This technique is also very difficult to control. Room air currents, mechanical vibrations, and other external factors affect the microlens formation. The inability to control these factors therefore severely limits the draw and lens technique in mass production facilities.
Mechanical machining entails machining, grinding, and polishing the optical fiber lens end. Mechanical machining provides flexible microlens configurations, but is excessively expensive. As a result, mechanical machining is not feasible for mass production processes.
Laser machining is similar to mechanical machining, but uses a laser such as a CO.sub.2 laser to ablate the fiber end. The laser machining technique can make a variety of microlens configurations and is less expensive than mechanical machining. This technique, however, has little use in a mass production environment. This is because each fiber must be fixed in a rotating stage and individually machined. The need to carefully process each fiber, therefore, makes volume production using laser machining impractical.
The bubble etch and lensing technique is a two-step process that etches the fiber to a point and then places the end of the fiber in an arc to form a hemispherical microlens. In the bubble etch and lensing technique, the optical fiber is etched in a bubble enclosure to keep hydrofluoric acid fumes from attacking the fiber above the taper. This method, like the laser machining method, possesses the problems of being labor intensive, difficult to control, having a low production yield, and only able to produce hemispherical microlenses.
In the taper etch and microlensing technique, the fiber is etched to a point using an oil boundary method instead of the bubble enclosure that the bubble etch and lensing technique uses. The fiber microlens is formed using an electric arc. While this process is easy to control and to scale for production volumes, the only microlens configuration that this process permits is hemispherical microlenses. It has been shown, however, that an ideal optical fiber microlens should have a hyperbolic microlens. This is because the ideal optical fiber lens should have an aperture large enough to collect all laser radiation. It should have a focal length that matches the laser and fiber modes. It also should be free of spherical aberrations. Moreover, an ideal optical fiber microlens should be coated to eliminate Fresnel reflections. H. M. Presby and C. A. Edwards in an AT&T Bell Laboratories "Electronic Letter" dated Mar. 12, 1992 illustrate that in order to meet these requirements the ideal shape for a microlens of a optical fiber cable is hyperbolic. None of the above described methods, however, provide a hyperbolic optical fiber microlens in a process that has significant application in a manufacturing environment.
Accordingly, there is a need for a method to produce an optical fiber lens that can produce a hyperbolic microlens in high production volumes.
There is a need for a method for producing an optical fiber microlens that accommodates large production volumes and that is flexible for a variety of microlens configurations.
There is a further need for a method for producing an optical fiber microlens that is easy to perform and to control and that manufacturing environment air currents, mechanical vibrations, or other external factors do not adversely affect.